'Illusion Coatings' Are Like Futuristic Camouflage

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Instead of using invisibility cloaks to conceal objects from
detection, "illusion coatings" could hide things by making them
look like something else, researchers say.

These illusion coatings could help soldiers or spies hide
antennas and sensors from remote inspection while still allowing
the devices to scan the outside world, the scientists added.

Invisibility cloaks, once thought of only as "Star Trek"
science fiction or "Harry Potter" fantasy, work by smoothly
guiding light waves around objects so the waves ripple along
their original paths as if nothing were there to block them.
Cloaking devices that work against other kinds of waves are
possible as well, such as the acoustic waves used in sonar.
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But one problem with invisibility cloaks is that they isolate
whatever they enclose. This means " the
act of cloaking would prevent an enclosed antenna or sensor
from communicating with the outside world," lead study author Zhi
Hao Jiang, an electrical engineer at Pennsylvania State,
said in a statement.

Instead, scientists have now developed what they call illusion
coatings — flexible, lightweight materials that can make whatever
they cover appear to be something other than what they really
are.

The investigators started with thin sheets of a composite
material composed of glass fibers and Teflon. These were covered
with patterns of copper stripes that interacted with the
composite material to scatter radio waves in a very precise way.
The stripes are only 35 microns deep and about 300 to 500 microns
wide. (For comparison, the average width of a human hair is 100
microns.)

Next, the researchers took whatever they want cloaked and
surrounded it with a separator — either air or foam. Finally,
they applied the coating. Depending on the copper patterns used,
the researchers could make a copper antenna or sensor look like
silicon or
Teflon when it was scanned by radio waves. They could also
make a Teflon cylinder look like a metal object.

These illusion coatings may one day help protect antennas and
sensors from discovery by hostile forces. "The coatings we
invented can still allow for the electromagnetic communication
between the coated object and the outside world," said study
co-author Douglas Werner, an electrical engineer at Pennsylvania
State University. "A sensor will be electromagnetically hidden or
camouflaged while it still maintains its sensing functionality."

Illusion coatings may also help protect any type of equipment
from stray or intentional
electromagnetic interference. For instance, they could help
enable multiple-antenna arrays, "where each antenna will not be
affected by the presence of the other antennas, even when they
are placed in very close proximity to each other," Werner said.

In addition, illusion coatings could be used for tasks other than
hiding. For example, they could help channel radio signals to
improve telecommunications, Werner said.

While these illusion coatings currently only work for radio
frequencies, the researchers are exploring ones that work against
infrared and visible wavelengths of light, Werner said.

The scientists will present their work in January at a meeting of
the Royal Society in Chicheley, England. The findings were
detailed online Oct. 9 in the journal Advanced Functional
Materials.